Process and device for controlling a vehicle braking system

ABSTRACT

A method and apparatus for controlling the brake system of a vehicle, in which pressure is built up and reduced in the wheel brakes by pulses having at least one changeable parameter. This at least one parameter is corrected as a function of at least one variable that influences the dynamics of the pressure change.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for controllinga brake system of a vehicle.

BACKGROUND INFORMATION

A conventional method and apparatus is described in German ApplicationNo. 41 23 783 (corresponding to U.S. Pat. No. 5,419,622). This GermanPatent Application describes a traction control system where at leastone driving wheel has the tendency to spin, and this wheel is brakedthrough the actuation of the associated wheel brake. The brake systemdisclosed in this document is a hydraulic brake system where pressure isbuilt up and reduced in the wheel brakes through activation of apressure-generating means (pump) and through actuation of a valvearrangement. To build up and reduce pressure within the framework of thetraction control system, in accordance with a conventional method, asequence of pressure-buildup pulses or pressure-reduction pulsesincluding pulses of predetermined length is established based on thedeviation of the wheel speed of the wheel tending to spin from areference speed.

The above-described conventional method and apparatus do not considerthat the dynamics of the pressure buildup or reduction is a function ofdifferent factors, such as temperature (outside temperature ortemperature of the hydraulics), a change in the base pressure broughtabout by the pressure-generating means, and/or the level of the voltagesupply of the pressure-generating means. Hence, there can be adeterioration of pressure-change dynamics in some cases.

It is therefore the object of the present invention to provide measuresfor improving the pressure-change dynamics.

In addition to the traction control system, pressure changes occur in atleast one wheel brake within the framework of other control orregulating systems, such as an anti-lock brake system, adriving-dynamics regulating system or an electrical brake control. Theseproblems can also occur in these areas of application, both in hydraulicand pneumatic brake systems.

SUMMARY OF THE INVENTION

The object of the present invention is to achieve a pressure-changedynamics in the control of a brake system which is satisfactory in alloperational situations.

One of the advantages is that the dynamic response of the pressurebuildup and reduction respectively, is effectively prevented fromdeteriorating under low temperatures, or given a change in the built-upbase pressure and/or a change in the supply voltage of thepressure-generating means; a satisfactory dynamic response is achievedin these operational situations.

Accordingly, significant improvements are made to the control system inwhich the means for achieving the object of the present invention arerealized.

The control systems which can benefit from the present invention includetraction control systems, anti-lock brake systems, driving-dynamicscontrol systems and/or pressure-control systems within the scope ofelectrically-controlled brake systems, both when working with hydraulicand pneumatic brake systems.

One advantage of the method and apparatus according to the presentinvention is that the temperature of the hydraulics or the outsidetemperature is detected by a corresponding sensor or estimated from therun-on behavior (or after-run effect) of the pressure-generating meansafter it has been shut off.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a control device for controlling a brakesystem according to the present invention.

FIG. 2 shows a flow chart of an embodiment of the present invention thatoperates as a program in a microcomputer that is a component of thecontrol device.

FIG. 3 a shows a first characteristic curve of a deviation at a drivingwheel over time and at a normal temperature.

FIG. 3 b shows a course of a wheel pressure corresponding to thecharacteristic curve illustrated in FIG. 3 a.

FIG. 3 c shows pressure-buildup pulses corresponding to the wheelpressure as illustrated in FIG. 3 b.

FIG. 4 a shows a second characteristic curve of the deviation at thedriving wheel over time and at a low temperature.

FIG. 4 b shows a course of the wheel pressure corresponding to thecharacteristic curve illustrated in FIG. 4 a.

FIG. 4 c shows pressure-buildup pulses corresponding to the wheelpressure as illustrated in FIG. 4 b.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a control device for a brake system thatexecutes a traction control, an anti-lock brake control, adriving-dynamics control and/or a control, depending on the driver'sbraking command, through a change in pressure in at least one wheelbrake. Shown are speed sensors 1–4, which are connected to the vehiclewheels and, via corresponding signal lines, to an electronic controlunit 5. Moreover, two wheel brakes 8 and 9 are shown, which areassociated with the driven vehicle wheels in the application of atraction control system. For the sake of a clarity, the wheel brakes ofthe other wheels are not shown in FIG. 1. Electrically-actuatable valvearrangements 6 and 7, which aid in controlling the pressure in the wheelbrakes, are associated with wheel brakes 8 and 9. The valve arrangements6 and 7 are respectively connected to the electronic control unit viaactuation lines 14 and 15. The valves are controlled using these linesfor building up and reducing pressure. Furthermore, a pressure source 10(e.g., a pump) is provided, which builds up a base pressure in the brakelines 16 or draws pressure medium from the brakes via return lines 21,22. This pressure source is connected via line 17 to the electroniccontrol device for actuation. Moreover, a line 18 leading from pressuresource 10 to the electronic control unit 5 transmits an index for thepump motor voltage (potential at a motor terminal). Furthermore, in oneembodiment according to the present invention, an input line 19 ofcontrol unit 5 is provided that connects the unit to a measuring device20 for detecting the ambient or hydraulics temperature, and/or thesystem pressure in brake lines 16. Further input lines, not shown, ofcontrol unit 5, for example an input line of a yaw-rate sensor, ofpressure sensors, etc., are provided in connection with otherapplications, e.g. a driving-dynamics control.

From the sensor signals of the wheel-speed sensors 1–4, the electroniccontrol unit 5 obtains control signals for the driven wheels. Thesecontrol signals indicate whether the tendency to spin exists at at leastone wheel (deviation BRA at wheel i>0). If this is the case, pulses aretransmitted by the control unit 5 via at least one of lines 14. Duringthe pulse time, these pulses bring valves 6 or 7 into the position inwhich pressure from pressure source 10 is introduced into brakes 8 or 9.If the control signal then disappears (BRA<0), correspondingpressure-reduction pulses are transmitted via at least one of lines 15to valves 6 or 7, which are actuated in the manner of a connection ofthe brake cylinders with return lines 21 and 22, only indicated here.

In one embodiment according to the present invention, when a deviationoccurs (BRAi>0) at at least one wheel, a first pressure-buildup pulsehaving a pulse length T1 becomes effective. If a deviation continues,further buildup pulses of predetermined length are emitted, and effect achange in pressure in the corresponding wheel brake, preferably equalchanges in pressure of, for example, 10 bar. These pressure-builduppulses are emitted until the deviation disappears. Afterward,pressure-reduction pulses are correspondingly generated for reducing thepressure that has built up in the wheel brake. With another occurrenceof a deviation, buildup pulses are again emitted, or the control isended when the deviation diminishes.

Correspondingly, pressure-buildup and pressure-reduction pulses aregenerated, depending on the driver's braking command, within theframework of an anti-lock brake control, a driving-dynamics control or apressure control.

Due to the temperature dependency of the hydraulic oil, of thevalve-opening times, of the pump delivery, etc., and the dependency ofthe pressure-buildup speed on the pressure generated by the pump, thepressure-buildup dynamics is not identical in all operationalsituations. The fundamental concept of the means for achieving theobject of the present invention, therefore, is to correct thepressure-buildup and pressure-reduction pulses as a function ofvariables that influence the dynamics of the pressure change. It isadvantageous to select the correction as a function of the temperatureof the ambient air or of the hydraulics, as a function of the supplyvoltage at the pump motor and/or of the system (base) pressure generatedby the pump.

The following values were obtained in an embodiment of a brake systemaccording to the present invention (Table 1):

Upump Temp. 9.5 V 13.0 V +20° 148 ms (factor 1.0)  123 ms (factor 1.0)−20° 396 ms (factor 2.67) 370 ms (factor 3.0) −30° 940 ms (factor 6.35) 808 ms (factor 6.57) (Upump: pump motor voltage; Temp: hydraulicstemperature)

In an embodiment according to the present invention, the temperature ofthe ambient air or the hydraulics is detected by an integral measuringdevice. In another embodiment according to the present invention, thetemperature is derived from the run-on of the pump. It has been seenthat the period of time between the pump shutoff and the point at whichthe pump motor voltage or the rotational speed of the pump falls below apredefined threshold value is a measure for the temperature of thehydraulics or the ambient air.

According to the present invention, the actuation times of the solenoidvalves are corrected by a factor when a low temperature is detected, sothat the corrected pulse length effects a predetermined pressure buildupin the respective wheel brake. The pulse lengths shown in the tableyield a pressure buildup of 10 bar. Correspondingly, a dependency on thepump motor voltage or on the system pressure of the pressure source isapparent. In this context, the lower voltage value shown in the tablerepresents a permissible limit value for the pump motor voltage. Belowthis voltage range, a fault condition is assumed.

FIG. 2 shows a flow chart to illustrate an implementation according tothe present means for achieving the object of the invention as acomputer program. After the program segment is started at predefinedpoints in time, wheel speed VRADi, pump motor voltage UPM and,optionally, temperature T of the ambient air or the hydraulics are readin during a first step 100. Thereafter, in step 102, deviation BRAi iscalculated for the driving wheels of the vehicle in a known manner,based on the wheel speeds VRADi. In the following step, 104,pressure-buildup or pressure-reduction pulses are formed for each wheelas a function of the determined deviation BRAi. In the following step,106, the correction values for the pulse length are determined from apredefined table as a function of the detected or estimated temperatureand/or the pump motor voltage; in the subsequent step, 108, the pulselength is correspondingly corrected, preferably through multiplicationor addition of the original pulse length and the determined correctionfactor, and transmitted to the valve arrangement of the wheel brake orbrakes. Thereafter, the program segment is ended and repeated in duecourse.

FIGS. 3 a–3 c and 4 a–4 c illustrate time diagrams that explain the modeof operation of the invention. FIGS. 3 a and 4 a respectively show thecharacteristic curve of the deviation BRAi at a driving wheel over time,while FIGS. 3 b and 4 b respectively show the corresponding course ofthe wheel pressure and FIGS. 3 c and 4 c respectively show thepressure-buildup pulses. FIGS. 3 a–3 c describe the situation involvinga normal temperature, while FIGS. 4 a–4 c describe illustrates alow-temperature situation.

From a specific point in time on, a driving wheel tends to spin. Thisincreases the deviation BRA for this driving wheel, as shown in theidentical representations in FIGS. 3 a and 4 a. Within the framework ofthe traction control system, pressure is built up for reducing thespinning tendency and for reducing the deviation through correspondingpulse actuation of the valves. FIG. 3 b shows the step-wise pressurebuildup corresponding to the emitted pulses. The pulses effecting thepressure buildup are shown in FIG. 3 c. They increase with an increasingpressure level, because the pressure-increase times become longer as aconsequence of the reduced pressure difference, and longer valve-openingtimes are then necessary for attaining a uniform pressure buildup.According to the present invention, the pulse length is corrected at lowtemperatures in response to the temperature, that is, it is prolonged inresponse to the pressure buildup. An objective according to the presentinvention is to attain the pressure increase that is provided at normaloperating temperatures, even at low temperatures. To attain a dynamicsin the pressure buildup that is comparable to that shown in FIG. 3 b,the pulse lengths are prolonged as shown in FIG. 4 c, starting from thepulse lengths of FIG. 3 c. In this context, the result is an increasingprolongation with an increasing original pulse length.

Such measures are also applied in the pressure reduction process.

The dependency of the pressure-buildup dynamics on the pump motorvoltage or on the attained system pressure yields corresponding results.

In another embodiment according to the present invention, the pause timebetween two pulses, or the frequency or period of the signal or,generally, the at least one changeable parameter of the at least onecontrol signal (also in the case of continuous control signals) isadapted, rather than the pulse length.

1. A method for controlling a brake system of a vehicle, the methodcomprising the steps of: obtaining at least one wheel speed, a pumpmotor voltage and at least one temperature parameter, the at least onetemperature parameter being at least one of an ambient air temperatureand a hydraulics temperature associated with the brake system;determining a deviation based on the at least one wheel speed;establishing a driving signal for the braking system based on the atleast one wheel speed for changing a braking pressure; determining acorrection value for correcting the driving signal based on the pumpmotor voltage and the at least one of the ambient air temperature andthe hydraulics temperature associated with the brake system; andcorrecting the driving signal based on the correction value.
 2. Themethod of claim 1, wherein the driving signal is a pulsed drivingsignal.
 3. The method of claim 2, wherein the pulsed driving signal iscorrected based on the correction value by changing a pulse length ofthe pulsed driving signal.
 4. The method of claim 3, wherein the step ofdetermining the correction value includes the step of obtaining anotherpulse length from a table of at least one of pulse lengths and actuationtimes.
 5. The method of claim 4, wherein the table includes at least oneof the pump motor voltage and the at least one temperature parameter. 6.The method of claim 4, wherein the table includes at least the pumpmotor voltage and the at least one temperature parameter.
 7. An controlarrangement for controlling a brake system of a vehicle, the controlarrangement comprising: a first arrangement for obtaining at least onewheel speed, a pump motor voltage and at least one temperatureparameter, the at least one temperature parameter being at least one ofan ambient air temperature and a hydraulics temperature associated withthe brake system; a second arrangement for determining a deviation basedon the at least one wheel speed; a third arrangement for establishing adriving signal for the braking system based on the at least one wheelspeed for changing a braking pressure; a fourth arrangement fordetermining a correction value for correcting the driving signal basedon the pump motor voltage and the at least one of the ambient airtemperature and the hydraulics temperature associated with the brakesystem; and a fifth arrangement for correcting the driving signal basedon the correction value.
 8. The control arrangement of claim 7, whereinthe driving signal is a pulsed driving signal.
 9. The controlarrangement of claim 8, wherein the pulsed driving signal is correctedbased on the correction value by changing a pulse length of the pulseddriving signal.
 10. The control arrangement of claim 9, wherein thefourth arrangement for determining the correction value includes anotherarrangement for obtaining another pulse length from a table of at leastone of pulse lengths and actuation times.
 11. The control arrangement ofclaim 10, wherein the table includes at least one of the pump motorvoltage and the at least one temperature parameter.
 12. The controlarrangement of claim 10, wherein the table includes at least the pumpmotor voltage and the at least one temperature parameter.